•••• "Nova: Engineering Ground Zero": About the rebirth of the WTC, but with science and great photograpny. 2 a.m., 2 p.m. Thursday.

•••• “9/11: The Days After”: A sequel to the 2008 “102 Minutes That Changed America,” it begins in the immediate aftermath of the collapse of the Twin Towers. Assembled mostly from home video and B-roll news footage, it proceeds without narration or talking heads. 9 p.m. Friday. History Channel's